Live data from Hacker News

Can a Human See a Single Photon? (1996)

math.ucr.edu

61–70 of 142 posts

Re: Can a Human See a Single Photon? (1996)

#61

I’ve been aware of this fact as Feynman points it out in the course of the lectures, but find it totally nuts — there is some sense of scale I’m missing. Matter consists of discrete chunks, atoms, but these chunks are so infinitesimal and numerous that there is no question of seeing them and any effect involving a handful of them is far, far below the human scale. Light also comes in chunks, and the number of these c…

I am not a physicist but fun fact, In transit there is no such thing as a photon(electro magnetic waves can transit at any energy level) however light can only interact with matter at discrete energy levels, so the photon(a discrete energy level of light) only exists there, at the interaction with matter.

For some very good practical optics you can do a lot worse than the Huygens Optics youtube channel. https://www.youtube.com/watch?v=SDtAh9IwG-I

Re: Can a Human See a Single Photon? (1996)

#62

Earlier quoted context omitted.

It is too bad the risks (criminal) are so high, LSD is an interesting enough experience that is worth trying at least once.

As someone who's never taken LSD and have talked to people who have, the number of times people express irreversible changes in how they think about things just from trying things once makes me think that it is not a very good idea to even try once. A chemical that causes irreversible random brain chemistry changes from a single use sounds like damage has happened and the user simply interprets that damage as an impr…

LSD as well as psilocybin and a number of other natural psychedelics exhibit what's called a "classical psychedelic effect". I've tried a couple of them and consider LSD to be essentially the same

It's worth noting that psychedelic fungi and plants are absolutely GLOBAL in distribution. Psilocybe can be found basically everywhere and there are a few related genera of fungi that also contain psilocybe. South America has a ton of psychedelic plants, but even Native America has some psychedelic grasses used to make "prairie ayahuasca". There's a ton of psychedelic cacti species including a very famous cactus (which I shall not name) that very few people know is psychoactive because the Native American group that uses it wishes to protect it from being overharvested. Some very poisonous plants like nightshade are also psychoactive. The fact that indigenous people throughout the Americas have managed to develop techniques to safely utilize these plants suggests close study and attention. There's a famous "Jesus was a mushroom" take by an archeologist that the early cults from which Christianity emerged dreamed up Jesus through their use of psychedelic mushrooms. The take doesn't hold much water but what is agreed upon is that even those groups regularly consumed psychedelics. Christmas also comes from cultural usage of psychedelics. Amanita muscaria, perhaps the most famous mushroom, is that red mushroom with the white spots (kinda looks like Father Christmas, don't it). It's poisonous and very psychedelic. To consume the psychoactive, indigenous European groups would drink reindeer piss. The piss neutralizes the poison but leaves the psilocybin. And so these reindeer allow Amanita muscaria to fly around dropping gifts for us.

I could go on about sweatlodges, the tens of thousands of different psychedelic plant species known, and other ways psychedelic experiences shaped cultures around the world.

My point is is that psychedelics are likely a universal cultural norm. In fact I'd argue we're living in a very strange culture where their use is not very widespread.

I personally didn't try a psychedelic until after highschool. My first experience cured my debilitating social anxiety and I went from my heart racing any time anyone talked to me to organizing community events within the span of a year. I've had similar effects with my depression and other mental health struggles. I'm not trying to suggest they're for everyone, but I'd say the fact that there's "irreversible changes in how [you] think about things" is exactly what makes them such a useful medicine

Re: Can a Human See a Single Photon? (1996)

#63
post #9

Earlier quoted context omitted.

Maybe seeing in the dark is simply so valuable that evolution has created extremely light-sensitive eyes for many species? If there was a molecule whose detection in tiny amounts would give a species a competitive edge, we might have noses capable of detecting 5-molecule amounts of this substance.

Weird that humans can do this when our eyes aren’t even that great at night vision compared to a lot of other animals.

Humans can navigate in darkness quite well if trained.

For vision, you look for shadows. Shadows are generally things that absorb light and reflect it, like trees.

Hearing can also tell you how close things are. In still air, a tree absorbs sound. Moving air flows around objects.

Then there is the feel of terrain underfoot. :)

Re: Can a Human See a Single Photon? (1996)

#64

Recent experiments have put the claim to test Overview https://www.nature.com/articles/nature.2016.20282 The actual work https://www.nature.com/articles/ncomms12172 > Here we report that humans can detect a single-photon incident on the cornea with a probability significantly above chance.

Interesting study, though if you look at the results 'significantly above chance' looks to be 0.60 +/- .05, which is indeed better than 0.50 but not what anyone could call reliable detection.

I wonder if trained owls could detect single photons, or if their night vision is based on just having much larger lenses that collect more light?

It seems that all rods in retinas are activated by single-photon-absorption, it's just about how many have to be activated to generate a neural signal.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4629483/

Re: Can a Human See a Single Photon? (1996)

#65
This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone.

You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blackbody_calculator/blackbody....

Re: Can a Human See a Single Photon? (1996)

#66

Earlier quoted context omitted.

It is too bad the risks (criminal) are so high, LSD is an interesting enough experience that is worth trying at least once.

As someone who's never taken LSD and have talked to people who have, the number of times people express irreversible changes in how they think about things just from trying things once makes me think that it is not a very good idea to even try once. A chemical that causes irreversible random brain chemistry changes from a single use sounds like damage has happened and the user simply interprets that damage as an impr…

"A chemical that causes irreversible random brain chemistry changes from a single use sounds like damage has happened"

From what I understand, LSD does not change your brain chemistry directly, but you make deep experiences, and those might change your deep thinking (and therefore the brain chemistry). Opening up your perception to other information channels. But sure, that doesn't mean it must be beneficial. And whether it is a damage I would say depends on the outcome.

I know people where LSD was beneficial (solving cluster headache or overcoming addiction) and people where it clearly wasn't (became spaced out weirdos). But everything you do or don't do, comes with a risk. If LSD does not appeal to you, then just don't do it.

Re: Can a Human See a Single Photon? (1996)

#67
> sensors in the retina can respond to a single photon. But neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms

Like an activation function in artificial neural networks

Re: Can a Human See a Single Photon? (1996)

#68

I’ve been aware of this fact as Feynman points it out in the course of the lectures, but find it totally nuts — there is some sense of scale I’m missing. Matter consists of discrete chunks, atoms, but these chunks are so infinitesimal and numerous that there is no question of seeing them and any effect involving a handful of them is far, far below the human scale. Light also comes in chunks, and the number of these c…

I'd need to verify my sources, but I recall the way photon detection works is by cascade; one photon comes in, and causes a couple of more "things" (I can't remember what - electrons, probably) to be dislodged, each of which causes a couple more... and boooom whooooosh very quickly you have something which can be easily noticed by a sensor.

Re: Can a Human See a Single Photon? (1996)

#69

Earlier quoted context omitted.

It is too bad the risks (criminal) are so high, LSD is an interesting enough experience that is worth trying at least once.

As someone who's never taken LSD and have talked to people who have, the number of times people express irreversible changes in how they think about things just from trying things once makes me think that it is not a very good idea to even try once. A chemical that causes irreversible random brain chemistry changes from a single use sounds like damage has happened and the user simply interprets that damage as an impr…

Who said it altered brain chemistry or that it would change you forever? I called it an interesting experience, that is it. Maybe for some people it is life changing, but then again some people say seeing the northern lights was life changing.

Re: Can a Human See a Single Photon? (1996)

#70
post #34

On a related note, you can hear sounds that displace your eardrums on the order of an atomic diameter. At least that is something I heard years ago, a quick search turned up this StackExchange question [1] so there may be some truth to this, I did however not read the answers too carefully. They actually seems to suggest that the threshold is even quite a bit smaller which makes me somewhat cautious of the claim, but…

>> sounds that displace your eardrums on the order of an atomic diameter.

That isn't all that surprising really. This isn't one atom moving a tiny bit. It is billions and billions of atoms all shifting back and forth together.

Post reply on HN